Many semiconductor processes require wafer measurements to be made from time to time for production-line quality control, product stability, and conformance to specifications. Generally, the processing results are evaluated after each significant step. Since many tests are destructive or will harm the product wafer, the measurements are typically performed on a test or “dummy” wafer, which are blank wafers that are mixed in with the product wafers. Dummy wafers are specially prepared to have similar characteristics as the product wafers. Typically, a dummy wafer is made of silicon, although other alternative materials have been described. Since silicon wafers are expensive, when the processing and testing is completed, the dummy wafers are usually cleaned, inspected, and reused. In the recovery or recycling of dummy wafers, it is important to provide a clean surface for subsequent processing. In the recycling of dummy wafers used in a masking photoresist process, it is important to completely remove blanket films of oxide and resist layers from the surface of the wafer down to the bare silicon.
Wet chemical processing is conventionally used for cleaning the surfaces of wafers. The cleaning is performed in order to produce a wafer having a silicon surface that is hydrophobic and repels water as the wafer is pulled out of the bath. The wafers are then rinsed in deionized water, dried in heated nitrogen gas (N2), and transferred to a processing operation, or stored.
Aqueous mixtures of hydrogen peroxide (H2O2) and sulfuric acid (H2SO4) are commonly used to strip or remove photoresist from a wafer surface after an etch processing step, or to remove a misaligned resist pattern from a wafer for re-imaging after development and inspection (“rework”). In such applications, it is desirable that the layer that is present under the resist, including, for example, silicon dioxide, remains intact on the wafer surface. In such cases, it is important to quickly remove the photoresist layer without attacking the underlying material. However, organic components in an underlying low-k dielectric layer, can alter the selectivity of the dielectric material to a resist layer.
In other applications, it is desirable to completely remove the oxide layer from a silicon surface. Hydrofluoric acid (HF) is conventionally used as a component of oxide etchants. HF solutions provide selective etch rates of about 100:1 or better for SiO2:Si, and effectively etch away the oxide but not the underlying silicon wafer material. Prevalent HF solutions include, for example, a 1:10 mixture of 49% hydrofluoric acid (HF) and water, and a dilute 1:6 aqueous mixture of HF and ammonium fluoride (NH4F). However, wet HF chemistries have difficulty removing low-k dielectrics such as a TMS-based low-k dielectric film, largely due to organic components in the oxide films. As a result, cleaning with an HF solution can leave the wafer with a gummy organic residue on the surface.
Therefore, it would be desirable to provide an improved composition for dissolution of low-k dielectric films from silicon-comprising surfaces. It would also be desirable to provide a cleaning composition that will completely remove low-k dielectric and photoresist components from the surface of a substrate such as a dummy wafer. It would also be desirable to provide a composition that can be modified to provide removal of a low-k dielectric material such as a TMS-based low-k dielectric film, from a wafer surface over a range of removal rates according to the application at hand.